These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Big Lipped Alligator Moment: There's a moment in Trigun Maximum where Vash and Livio are counting the coins they got from the Gung-ho guns. They were missing one. Suddenly, a muscular black guy with weird hair and skimpy disco attire comes in and gives them the coin, pulls a bug out of his mouth, then proceeds to ask whether Vash or Livio prefer clams or fish. Granted, there's a reason why this happened (Zazie used her mind control worms), but it's random, it's weird, and after the incident, nobody talks about it again.
Creepy Awesome: Legato, who is a fan favourite because of his disturbing mein, creepy voice, and love of tormenting Vash.
Destructive Savior: Saving people but destroying their property will mean that even the people you save will just hate you. Indeed, the more destruction you cause, the more you will be seen as a bad guy and not as a hero, no matter how many lives you save.
Save the Villain: Just because you won't kill the mass-murdering psychopath or the slave trader or whatever, it doesn't mean they will reform. No, not even if you risk your life to save theirs. Also, it makes you responsible for any crimes that they go on to commit, because you deliberately gave them the chance to keep on committing crime.
Thou Shalt Not Kill: Just because you refuse to kill doesn't mean that others will choose to follow your highly idealistic philosophy. Indeed, following this philosophy will not only cost you dearly, but make you less effective at actually stopping suffering and misery than being willing to kill does, because some people are so irredeemably evil that the only way they will stop causing misery is when they are dead.
Draco in Leather Pants: Almost too many to count. Legato makes fangirls pass out all over the place (even though he's gay, and was even a gigolo — only in the manga, though). Knives has a fervent fandom too. Which is especially creepy given it's implied that they're both cannibals.
Also, Livio in the manga, goes from a wild card to The Lancer after Nicolas' death.
Evil Is Sexy: Legato, Knives, and a few of the more minor Gung-Ho Guns may count. Legato in particular is a pretty extreme case considering he's probably the evilest character in the story...and also probably one of if not the best-looking (which really says a lot).
Fan Wank: Not as bad as in other fandoms, but still pretty bad at times.
Foe Yay: Particularly egregious when Legato seems to be hitting on Vash. It's made stronger by the fact that Legato genuinely is gay and he also is fixated upon Knives, who is Vash's identical twin.
"Funny Aneurysm" Moment: When someone says that the cross Wolfwood carries on his back is heavy he replies "That's because it's full of mercy!" Later on, that line becomes a bit sinister.
Germans Love David Hasselhoff: Trigun is ridiculously popular in America, but not quite as much in its homeland of Japan. Because of this, the movie premiered at Sakuracon 2010, months before the Japanese premiere.
Growing the Beard: The anime starts out as goofy, almost slice of life style misadventures as Vash roams the desert getting into trouble while Merril and Milly desperately chase after. Then it turns into a darker, grittier story as Vash's Evil Twin rears his sinister head and Vash in caught up in a dark and horrible story of Sibling Rivalry that examines just how much a person can really expect to uphold the ideal of Thou Shalt Not Kill.
For Vash specifically, this might be better termed Showing the Beard, as he's actually quite competent from the very start, he's just a CloudCuckoolander/prime example of Obfuscating Stupidity most of the time so it's not terribly obvious. Opinions vary as to exactly where this happens in the anime, but it's pretty early; brief flashes of Vash's badassery appear as early as the end of Episode 2, and very few would put it later than Episode 5.
Ho Yay: Vash and Wolfwood have a lot of romantic-ish interactions with each other.
Iron Woobie: Vash, apparently. Seriously, nothing is allowed to go right in his life, and he loses everything and takes it very much on his own head whenever anyone gets hurt on a half-civilized planet with almost no natural resources and loads of guns. And it took him over a hundred years to briefly give up.
It Was His Sled: Most of the anime's big twists have long since passed into common knowledge in the English-speaking anime community by now, to the extent that when [adult swim] chose one episode to air for their 2012 April Fool's Day Toonami block, it was the one where Wolfwood dies.
Moe: Let's face it, Vash is a very Moe character. You just have to see the visceral Squees he seems to trigger all over the fandom.
Narm Charm: Debatable too — Vash and Knives's whining pathetic ways of arguing about their very extreme ideologies bring out their emotional immaturity, as they can't seem to get more nuanced than "everybody is good vs. everybody is evil."
After Wolfwood's death, Vash is eating donuts in a lively, ordinary town, remarking at how wonderful being alive is and at all the people. He then suddenly breaks down in tears as he thinks of all the horrible things that have happened to him, as well as the fact that many of his friends are now dead. And then Legato shows up.
Unfortunate Implications: Legato, who may or may not be the show's only canonically gay character, is a sadistic mass murderer who was sexually abused as a child. Ouch!
Also, the manga's only transsexual character is also a depraved mass-murdering killer.
The show also seems to have some less-than-progressive attitudes toward women: on the one hand, Meryl and Millie are certainly presented as fairly independent and capable; on the other hand, they're still fairly ineffectual compared to the most important male characters, and the most physically-powerful woman we see (Dominique the Cyclops) is an antagonist who only gets one episode to show her stuff and dies in short order afterward.
The anime also features Vash missing a chance to attack her to instead rip the buttons off her shirt and say "I could have groped you four times"[in that instant you attacked me]. And then he says that a beautiful woman like her shouldn't be fighting but should be keeping house for her man, in a tone as if it's a horrible depressing thing that a lady is FORCED to fight against her will instead of having his idea of a woman's perfect life. Nothing in the show even indicates that she didn't choose to become a Gung-Ho Gun, let alone that she has a husband or wants one.
Some parents consider this to be an anime for teens ages 15-16 when it's more specifically created for kids around their early teens. Some people do consider this anime for kids, but since it's aimed at kids a little younger compared to Cowboy Bebop, it could also be for a preteenage group.